Eliminating unwanted reactance at high frequencies is a perennial design challenge. Circuits operating at high frequencies have many special design considerations, both for the devices and for the circuits. Inductance is a cause of reactance, i.e. the way a circuit "reacts" to changes in alternating current or voltage. Devices have characteristic inductance: a characteristic tendency to impede change in current passing through the device or component. The resistance to change, i.e. this sort of inertia or sluggishness, must be minimized especially in high frequency devices in order that suitable performance can be attained. Components in high frequency applications often require low inductance interconnects.
"Slab line" transmission lines are commonly used in the construction of microwave and millimeter wave frequency components. These transmission lines typically have a center conductor of round or rectangular cross section which is generally placed equidistant from two parallel conducting ground plates.
The end of the slab line center conductor often must be terminated in resistance equal to the line's characteristic impedance to avoid reflection. Moreover slab line components including ground plates often need to be removed during assembly or rework.
Previous approaches to slab line termination required the thin film termination circuit to be soldered into a round outer cartridge. The cartridge was then inserted from a outer edge of the component. Contact to the slab line center conductor was effected through a springy bellows or collet contact placed in the end of the center conductor. In order to operate at frequencies above 100 GHz, the center conductors must be of very small cross section and bellows and collets are not available in this size range.
Another approach to slab line termination required the vertical installation of the circuit between two conducting planes. This configuration precludes easy removal or reinstallation of the ground planes. Such removal or reinstallation capability is often an important feature, especially for assembly or reworking.
What is needed is a low inductance interconnect operable at microwave and millimeter wave frequencies that is easy to rework during test and assembly. It is also desirable that such a connection provide terminal resistance matching or equal to characteristic impedance. Further, it is desirable that such a connection be manufacturable at and within the dimensions required for microwave connections.